The present invention relates to a waveform generation apparatus and method for generating, transmitting, and synthesizing plural binary-state signals to generate a multi-valued composite signal and, more particularly, to a waveform generation apparatus having a construction for eliminating an adverse effect of phase differences among the plural binary-state signals on the multi-valued composite signal.
In recent years, high-density recording on recording media has been demanded for an increase in recording capacity, and an improved accuracy of waveform generation has been demanded of waveform generation apparatuses for an increase in recording density.
FIG. 13 is a block diagram illustrating the construction of a conventional waveform generation apparatus. The conventional waveform generation apparatus is provided with a delay circuit 501 comprising plural stages of delay elements which are connected in series; plural (k pieces of) selectors 502-1xcx9c502-k for selecting the outputs from the respective output stages of the delay elements constituting the delay circuit 501; a waveform generation circuit 504 for receiving the outputs from the plural selectors; a transmission path 505 for transmitting the outputs from the waveform generation circuit 504; a waveform synthesis circuit 506 for synthesizing the waveforms of the signals transmitted through the transmission path 505; and plural (k pieces of) selector control circuits 507-1xcx9c507-k for controlling the operations of the respective selectors.
Hereinafter, the operation of the conventional waveform generation apparatus constructed as described above will be described.
When a recording/playback medium such as an optical disc is continuously irradiated with a laser beam for the duration of forming recording marks on the medium, heat generated by the irradiation with the laser beam stays on the medium, and the recording marks become larger with time, resulting in tear-drop-shaped marks as shown in FIG. 14. Thus, the recording/playback medium has a problem caused by the physical phenomenon on the medium.
If data are written on the recording/playback medium in which the problem caused by the physical phenomenon remains, the data cannot be read normally when the medium is played back. Therefore, it becomes necessary to generate a recording waveform so as to correct the physical phenomenon at recording. In the case of an optical disc, for example, a recording waveform is generated so as to frequently turn on and off a laser beam. Thus, it is necessary to generate a recording waveform for correction suited to each recording medium.
When generating such recording waveform for correcting the physical characteristics of a recording medium it becomes necessary to generate reference timings (reference clocks for recording correction) which are finer than a reference clock for writing.
In order to generate reference clocks for recording correction, delayed clocks are generated by delaying a reference clock with the delay circuit 501, and timings corresponding to the delay amounts are generated. Which delayed clock (delay amount) among the delayed clocks generated in the delay circuit 501 is to be adopted depends on the select state of each of the k pieces of selectors 502-1xcx9c502-k.
The waveform generation circuit 504 generates plural recording waveforms having different binary states, using the selected clocks having different delay amounts, according to input data. The recording waveforms having different binary states are transmitted through the transmission path 505. The waveform synthesis circuit 506 synthesizes binary-state signals corresponding to three recording waveforms among the transmitted recording waveforms having different binary states, thereby forming a multi-valued signal for recording. The multi-valued signal is transmitted to a laser diode (not shown) in the subsequent stage, whereby the laser diode is driven and data writing is carried out The reason why the multi-valued signal is not directly transmitted to the transmission path 505 is because data transmission errors due to noise are increased if multi-valued signal is transmitted through the path 505. So, the binary data (binary-state signals) are transmitted through the path 505 to reduce the errors due to noise. Furthermore, the selector control circuits 507-1xcx9c507-k control the respective selectors 502-1xcx9c502-k so as to select the delay amounts according to the setting of waveform generation.
In the conventional waveform generation apparatus constructed as described above, the paths of the respective binary-state signals up to the waveform synthesis circuit 506 will vary, when the signals from the delay circuit 501 are trasmitted through the respective selectors 502-1xcx9c502-k, the waveform generation circuit 504, and the transmission path 505, to the waveform synthesis circuit 506, resulting in skews among the signals. Therefore, it is necessary to adjust the lengths of the respective paths or the numbers of circuits through which the respective signals pass, thereby to minimize the skews.
Even when the transmission paths or the like are adjusted to minimize the skews, the delay amounts in the respective paths or circuits may vary due to the temperature, voltage, passage of time, or the like, and the variations appear as skews. These skews among the respective signals cause errors in the recording waveforms even though the signal inputs to the waveform generation circuit 504 are accurately controlled using the delay circuit 501 as shown in FIG. 13, resulting in errors in th recording marks.
In the conventional waveform generation apparatus and method constructed as described above, although the highly-accurate clocks are inputted to the waveform generation circuit 504 by using the delay circuit 501 and the selectors 502-1xcx9c502-k, skews are generated due to factors such as the signal transmission paths, use environment, passage of time, and the like, resulting in errors in recording waveforms.
The present invention is made to solve the above-mentioned problems and has for its object to provide a waveform generation apparatus and method which can reduce errors in recording waveforms due to skews among binary-state signals.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a first aspect of the present invention, there is provided a waveform generation apparatus for transmitting in pieces of binary-state signals, and generating a signal waveform having a multi-valued state by synthesizing the n pieces of binary-state signals, which apparatus comprises: a delay means comprising i pieces of unit delay circuits connected in series, and providing i kinds of delay states by deriving signals from the respective unit delay circuits; k pieces of selection means each selecting one delay state from among the kinds of delay states of the delay means; a waveform generation means for generating n pieces of binary-state signals in the same state, or generating n pieces of binary-state signals having a shape according to recording data supplied from the outside, on the basis of the signals having the i kinds of delay states, which are outputted from the k pieces of selection means, and the recording data supplied from the outside; a transmission means for transmitting the n pieces of binary-state signals generated by the waveform generation means; a waveform synthesis means for generating a signal having multi-valued information from the n pieces of binary-state signals transmitted by the transmission means; a phase difference detection means for detecting phase differences among the n pieces of binary-state signals in the same state, when the n pieces of binary-state signals in the same state are transmitted through the transmission means; and an offset control means for controlling the k pieces of selection means on the basis of phase difference information from the phase difference detection means, and adding offset values to target delays, thereby to eliminate the phase differences among the signals in the transmission means. Therefore, with respect to transmission of the n pieces of binary-state signals, skews among the respective signals can be controlled and absorbed as offsets of the delay means, thereby improving composition accuracy of a composite waveform which is generated from the n pieces of binary-state signals.
According to a second aspect of the present invention, in the waveform generation apparatus according to the first aspect, the phase difference detection means comprises: a most delayed signal detection means for detecting a signal which is transmitted most lately, from among the n pieces of binary-state signals transmitted by the transmission means; a state storage means for storing the result of the detection by the most delayed signal detection means; and a delay amount calculation means for calculating a difference in delay amounts between the most-lately transmitted signal stored in the state storage means and another signal. Therefore, skews among the n pieces of binary-state signals can be reduced by detecting a signal which is transmitted most lately from among the n pieces of binary-state signals, and setting an offset delay of another signal to the latest signal, thereby improving composition accuracy of a composite waveform which is generated from the n pieces of binary-state signals.
According to a third aspect of the present invention, in the waveform generation apparatus according to the first aspect, the waveform generation means generates the n pieces of binary-state signals on the basis of the k pieces of signals selected by the selection means, and the input data; and the offset control means comprises: a path switching means for successively selecting all paths in the waveform generation means, through which the k pieces of signals selected by the selection means and the input data are transmitted; and a path offset storage means for holding offset information when the path switching means selects a path. Therefore, skews among the n pieces of binary state signals can be adjusted in all of the waveform generation modes, whereby composition accuracy of a composite signal generated from the n pieces of binary-state signals can be improved in all of the waveform generation modes.
According to a fourth aspect of the present invention, in the waveform generation apparatus according to the first aspect, the offset control means comprises: a unit delay amount calculation means for calculating a delay amount for each stage of unit delay circuit of the delay means; and an offset conversion means for converting the difference in delay amounts which is obtained by the phase difference detection means, into an offset value of the selection means, on the basis of the delay amount for each stage of unit delay circuit, which is obtained by the unit delay calculation means. Therefore, the offset control means can calculate as to which of the outputs from the i stages of delay means is to be employed by the selection means in the calculation of the delay amount per stage of delay means, whereby the selection of the selection means is facilitated, and composition accuracy of a composite waveform is improved.
According to a fifth aspect of the present invention, the waveform generation apparatus according to the first aspect further comprises a clock signal generation means for generating predetermined clock signals; the waveform generation means continuously receives two clock signals generated by the clock signal generation means, and outputs the clock signals to the transmission means; and the phase difference detection means detects phase differences among the n pieces of binary-state signals in the same state, and a phase difference between the continuously inputted two clock signals. Therefore, with respect to transmission of the n pieces of binary-state signals, skews among the respective signals can be controlled and absorbed as offsets of the delay circuit, and decision as to whether the offset control should be carried out or not is implemented by continuously detecting a skew between the two clock signals which are transmitted through the transmission path, whereby the frequency of skew correction is increased, and composition accuracy of a composite signal generated from the n pieces of binary-state signals is improved.
According to a sixth aspect of the present invention, in the waveform generation apparatus according to the fifth aspect, the waveform generation means is provided with a waveform generation state detection means for detecting a state where there is no data input and no waveform generation should be carried out. Therefore, offset correction is executed automatically, whereby the frequency of skew correction is increased, and composition accuracy of a composite waveform generated from the n pieces of binary-state signals is improved.
According to a seventh aspect of the present invention, in the waveform generation apparatus according to a fifth aspect, the offset control means is provided with a phase difference level detection means for detecting that the phase difference between the continuously-transmitted two clock signals becomes larger than a predetermined value; and when the offset control means receives a signal indicating that the state where no waveform generation should be performed is detected, from the waveform generation state detection means, and a signal indicating that the phase difference becomes larger than the predetermined value, the offset control means performs the process of adding offset values to target delays. Therefore, skew correction can be automatically carried out while continuously checking as to whether skew differences in the transmission path are caused by temperature or voltage, whereby the frequency of skew correction is increased, and composition accuracy of a composite waveform generated from the n pieces of binary-state signals is improved.
According to an eighth aspect of the present invention, there is provided a waveform generation method for transmitting n pieces of binary-state signals, and generating a signal waveform having a multi-valued state by synthesizing the n pieces of binary-state signals, which method comprises: a delay step of deriving signals from arbitrary number of stages of unit delay circuits which are connected in series, and outputting signals having i kinds of delay states; a selection step of selecting predetermined delay states from among the i kinds of delay states; a waveform generation step of generating n pieces of binary-state signals, on the basis of the signals having the predetermined delay states which are selected from among the i kinds of delay states, and data input; a transmission step of transmitting the n pieces of binary-state signals generated in the waveform generation step, onto a transmission path; a waveform synthesis step of generating a signal having multi-valued information, from the n pieces of binary-state signals generated in the waveform generation step and then transmitted; a step of outputting signals in the same state as n pieces of binary-state signals; a phase difference detection step of detecting phase differences among the n pieces of binary-state signals in the same state, when the n pieces of binary-state signals in the same state are transmitted through the transmission step; and an offset control step of controlling the number of delay stages in the delay step on the basis of phase difference information from the phase difference detection step, and adding offset values to target delays, thereby to eliminate the phase differences among the signals in the transmission step. Therefore, with respect to transmission of the n pieces of binary-state signals, skews among the respective signals can be controlled and absorbed as offsets in the delay step, thereby improving composition accuracy of a composite waveform which is generated from the n pieces of binary-state signals.
According to a ninth aspect of the present invention, in the waveform generation method according to the eighth aspect, the phase difference detection step includes: a most delayed signal detection step of detecting a signal which is transmitted most lately, from among the n pieces of binary-state signals transmitted in the transmission step; a state storage step of storing the result of the detection in the most delayed signal detection step; and a delay amount calculation step of calculating a difference in delay amounts between the most-lately transmitted signal stored in the state storage step and another signal. Therefore, skews among the n pieces of binary-state signals can be reduced by detecting a signal which is transmitted most lately from among the n pieces of binary-state signals, and setting an offset delay of another signal to the latest signal, thereby improving composition accuracy of a composite waveform which is generated from the n pieces of binary-state signals.
According to a tenth aspect of the present invention, in the waveform generation method according to the eighth aspect, in the waveform generation step, the n pieces of binary-state signals are generated on the basis of k pieces of signals selected in the selection step, and the input data; and the offset control step includes: a path switching step of successively selecting all paths in the waveform generation step, through which the k pieces of signals selected in the selection step and the input data are transmitted; and a path offset storage step of holding offset information when a path is selected in the path switching step. Therefore, skews among the n pieces of binary state signals can be adjusted in all of the waveform generation modes, whereby composition accuracy of a composite signal generated from the n pieces of binary-state signals can be improved in all of the waveform generation modes.
According to an eleventh aspect of the present invention, in the waveform generation method according to the eighth aspect, the offset control step includes: a unit delay amount calculation step of calculating a delay amount for each stage in the delay step; and an offset conversion step of converting the difference in delay amounts which is obtained in the phase difference detection step, into an offset value in the selection step, on the basis of the delay amount for each stage in the delay step, which is obtained in the unit delay calculation step. Therefore, the offset control step can calculate as to which of the outputs from the i stages of delay means is to be employed in the selection step for the calculation of the delay amount per stage of delay means, whereby the selection in the selection step is facilitated, and composition accuracy of a composite waveform is improved.
According to a twelfth aspect of the present invention, there is provided a waveform generation method for transmitting n pieces of binary-state signals, and generating a signal waveform having a multi-valued state by synthesizing the n pieces of binary-state signals, which method comprises: a delay step of deriving signals from arbitrary number of stages of unit delay circuits which are connected in series, and outputting signals having i kinds of delay states; a selection step of selecting predetermined delay states from among the i kinds of delay states; a waveform generation step of generating n pieces of binary-state signals, on the basis of the signals having the predetermined delay states which are selected from among the i kinds of delay states, and data input, and continuously transmitting two clock signals; a transmission step of transmitting the n pieces of binary-state signals generated in the waveform generation step, and the continuously supplied two clock signals, onto a transmission path; a waveform synthesis step of generating a signal having multi-valued information, from the n pieces of binary-state signals generated in the waveform generation step and then transmitted; a step of outputting signals in the same state as n pieces of binary-state signals; a phase difference detection step of detecting phase differences among the n pieces of binary-state signals in the same state, and detecting a phase difference between the continuously supplied two clock signals, when the n pieces of binary-state signals in the same state are transmitted through the transmission step; and an offset control step of controlling the number of delay stages in the delay step on the basis of phase difference information from the phase difference detection step, and adding offset values to target delays, thereby to eliminate the phase differences among the signals in the transmission step. Therefore, with respect to transmission of the n pieces of binary-state signals, skews among the respective signals can be controlled and absorbed as offsets in the delay step, and decision as to whether the offset control should be carried out or not is implemented by continuously detecting a skew between the two clock signals which are transmitted through the transmission path, whereby the frequency of skew correction is increased, and composition accuracy of a composite signal generated from the n pieces of binary-state signals is improved.
According to a thirteenth aspect of the present invention, in the waveform generation method according to the twelfth aspect, the waveform generation step includes a waveform generation state detection step of detecting a state where there is no data input and no waveform generation should be carried out. Therefore, offset correction is executed automatically, whereby the frequency of skew correction is increased, and composition accuracy of a composite waveform generated from the n pieces of binary-state signals is improved.
According to a fourteenth aspect of the present invention, in the waveform generation method according to the twelfth aspect, the offset control step includes: a phase difference level detection step of detecting that the phase difference between the continuously-transmitted two clock signals becomes larger than a predetermined value; and an adjustment decision step of detecting the state where no waveform generation should be performed, from the waveform generation state detection step in the waveform generation step, and adjusting the n pieces of binary-state signals. Therefore, skew correction can be automatically carried out while continuously checking as to whether skew differences in the transmission path are caused by temperature or voltage, whereby the frequency of skew correction is increased, and composition accuracy of a composite waveform generated from the n pieces of binary-state signals is improved.